The WhatsApp instant messaging service is on course to connect one billion people around the world, Facebook founder Mark Zuckerberg has said.
The mobile phone application was bought by Facebook for 19 billion US dollars (£12 billion) last week.
It was announced today that a voice calling service will be added to WhatsApp in the coming months.The WhatsApp brand is to be maintained and its headquarters will remain in Mountain View, California. Its co-founder and chief executive Jan Koum will join Facebook's board of directors.
Mr Koum told the conference that WhatsApp would offer a voice service for Android mobiles and iPhones this spring, with Blackberry, Microsoft and Nokia handsets coming later.
Some WhatsApp users are apparently still experiencing problems with the instant messaging service, following a message posted from its official Twitter account to say that problems had been resolved after a two-hour outage.
WhatsApp took to Twitter to complain about the problems with the instant messaging service, while others joked that the app's recent multi-billion dollar deal with Facebook was behind the two-hour outage.